Method of stabilizing unsaturated organic compounds from polymerization

ABSTRACT

A method for stabilizing an unsaturated polymerizable organic compound from premature polymerization includes addition thereto of an imidazoline or imidazolidine compound, optionally with ring substituents including hydroxyl, oxyl, or oxide moieties as well as aliphatic, alicyclic and/or heterocyclic moieties.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to a method for stabilizing unsaturatedorganic compounds from polymerization and to a monomeric compositioncontaining a polymerization inhibitor.

2. Background of the Art

The ethylenically unsaturated compounds which can be polymerized by freeradical initiation are commonly called monomers. They constitute a majorclass of industrial chemicals. Because of the presence of thepolymerizable double bond, the widespread sources of initiating radicalsfrom peroxides, light and/or thermal generation, such monomers are proneto undesirable and premature polymerization at various stages duringtheir manufacture, purification, storage, shipping, blending and use.Protection of such monomers from such premature polymerization is neededup to the point where polymerization is actually desired. If prematurepolymerization does occur, the monomer may suffer contamination bypolymer, troublesome increase in viscosity, gelation and/or loss ofreactivity. Fouling of distillation equipment including heat exchangersurfaces, storage vessels, transfer lines, pumps, shipping containersand application equipment can occur with ensuing costs of cleaning,downtime, loss of material and unnecessary labor costs. Prematurepolymerization can also constitute a safety hazard since uncontrolledexothermic polymerization can cause ruptured vessels, atmosphericcontamination, and in extreme cases, explosions and fires. Deteriorationof monomers in shipping and storage may also make necessary the use ofcostly refrigerated shipping and storage facilities.

A further problem is that of undesired free radical polymerization ofunsaturated monomers which occur in commercial products such ashydrocarbon fuels and refinery streams. In these cases, polymerizationaccompanied by the incorporation of oxygen moieties leads to gum andsludge deposits which can foul carburetors, engines, fuel tanks or fuellines. In refineries, such monomers in hydrocarbon streams such ascracking products can foul pipelines, valves, pumps, heat exchanges,stills and storage vessels.

Another problem in regard to undesired polymerization of free radicalpolymerizable monomers is the case of polymerizations which areintentional, but which must be prevented from going too far. Forexample, the quality of poly(vinyl chloride) suspension polymer and ofsynthetic rubber made from olefins and dienes is superior (i.e. bettermolecular weight distribution, stability, and processing properties) ifthe polymerization is stopped short of complete consumption of themonomers. It is also desirable to have available in a plant conductingvinyl polymerization reactions some rapid and efficient means forstopping a runaway polymerization if other means such as cooling shouldfail.

It is known that the addition of certain compounds to monomers canretard or even prevent their undesired polymerization, and that whenpolymerization of the monomer is desired, the inhibitor can be removedor overridden by a deliberately-added polymerization initiator. Variousaromatic compounds have been used as such inhibitors in the prior art.Typical ones are 2,6-dinitro-p-cresol (DNPC), hydroquinone, monomethylether of hydroquinone (MEHQ), tert-butylphenols, phenothiazine,phenylenediamines and benzoquinones. These are usually used at a levelof 50 to 1000 ppm. These inhibitors are not totally effective, and evenwith such inhibitors present it is often advisable to store suchinhibited monomers in a cool place and for limited periods of time.Moreover, these aromatic inhibitors are a cause of serious discolorationproblems in the monomers and in polymers deliberately prepared from suchmonomers. Typically these aromatic inhibitors produce quinoidalchromophoric groups with very visible light absorbance.

Various other polymerization inhibitors are known. For example, U.S.Pat. No. 5,258,138 to Gatechair et al. discloses the stabilization ofethylenically unsaturated monomers from premature polymerization byadding to the monomer a stabilizing amount of a substituted hinderedamine in combination with phenothiazine or other related heterocyclicmoiety.

U.S. Pat. No. 4,670,131 to Ferrell discloses that fouling of equipmentused for processing organic feed streams containing olefinic compoundscan be controlled by inhibiting polymerization of the olefinic compoundsby the addition of a stable free radical such as a nitroxide to thefeedstream.

SUMMARY

In accordance with the present invention a method for stabilizing apolymerizable unsaturated organic compound from premature polymerizationis provided. The method comprises:

adding to the unsaturated organic compound an effective amount,sufficient to prevent premature polymerization, of at least onepolymerization inhibitor having the formula:

wherein X is —H, —OH, —O•, —NO₂, or —CH₃,

R¹ R², R⁴ and R⁵ are the same or different and each is selected from thegroup consisting of hydrogen, an aliphatic moiety having from 1 to about20 carbon atoms, aryl, alkaryl or aralkyl having from 6 to about 12carbon atoms, alicyclic and heterocyclic, or wherein R¹ and R² togetheror R⁴ and R⁵ together form part of an alicyclic or heterocyclic moietyhaving from about 4 to about 10 ring members,

R³ and optional group R⁶ are the same or different and each ispreferably selected from the group consisting of hydrogen, an aliphaticmoiety having from 1 to about 20 carbon atoms, or wherein R³ and R⁶together represent oxygen in the form of an oxo (═O) moiety,

and wherein the dotted lines each represent an optional supplementalbond, such that where there is no optional supplemental bond within thering the R⁶ group is present as a ring substituent, z is 1 and Y is —H,—OH, or —O•, and where there is an optional supplemental bond within thering, there is no R⁶ group present as a ring substituent, z is 0 or 1and where z is 1, Y is O bonded to N in the form of an N→O moiety.

Also provided herein is a composition which includes an ethylenicallyunsaturated monomer and an effective amount of the polymerizationinhibitor described herein.

DETAILED DESCRIPTION

The present method for stabilizing a polymerizable unsaturated organiccompound from premature polymerization comprises adding to theunsaturated organic compound an effective amount of a polymerizationinhibitor which includes an imidazoline or imidazolidine compound,optionally with hydroxy, oxo, oxyl or oxide substituents, as describedmore fully below.

The polymerizable organic compound is preferably an ethylenicallyunsaturated monomer having at least one carbon-carbon double bondcapable of undergoing free radical induced polymerization. Particularlyadvantageous is the stabilization of styrene. The unsaturated organiccompound can be neat (i.e., undiluted) or admixed with a solvent such astoluene, benzene, ethylbenzene, styrene or water.

Typical examples of such monomers are olefinic and vinyl aromaticcompounds including, but not limited to, styrene, methylstyrene,divinylbenzene, dienes such as butadiene and isoprene; halogenatedmonomers such as vinyl chloride, chloroprene, vinylidene chloride,vinylidene fluoride and vinyl fluoride; unsaturated acids such asacrylic acid, methacrylic acid and crotonic acid; unsaturated esterssuch as vinyl acetate, alkyl acrylates and alkyl methacrylates such asmethyl methacrylate, ethyl acrylate, methyl acrylate, 2-hydroxyethylacrylate and methacrylate, ethylene bismethacrylate, trimethylolpropanetriacrylate, acrylated epoxy resin and polyethylene glycol diacrylate;unsaturated amides such as acrylamide, N,N-dimethylacrylamide,methylene-bisacrylamide and N-vinylpyrrolidone; unsaturated nitrilemonomers such as acrylonitrile; and unsaturated ethers such as methylvinyl ether; and miscellaneous monomers such as the vinyl pyridines,diethyl vinylphosphonate and sodium styrenesulfonate.

The method of the instant invention involves simply dissolving aneffective inhibiting amount of the inhibitor in the monomer prior toexposure of the latter to conditions where the premature, undesired freeradical initiated polymerization might occur.

The polymerization inhibitor can be added prior to any processing stepsfor example to extend storage life. Alternatively the polymerizationinhibitor can be added in any part of the processing equipment, forexample to deactivate autocatalytic polymerization of any unsaturatedmonomer present in the feed stream.

By “effective amount” is meant an amount or concentration sufficient toprevent premature polymerization of the monomer. An effectiveconcentration of the polymerization inhibitor described below can rangefrom 1 ppm to about 10,000 ppm by weight of polymerization inhibitor inthe monomer, preferably about 10 ppm to about 1,000 ppm, and morepreferably about 50 ppm to about 200 ppm. The lower amount would be usedwhere the degree of inhibition is not great, such as when the monomer isto be used promptly and/or will be stored in a refrigerator, or wherethe monomer is inherently less prone to polymerize readily, such asthose compounds with internal double bonds. Higher concentrations ofinhibitor are used where the monomer is stored for long periods of timeor in warm conditions, where contamination is likely, where the monomeris likely to be exposed to photoinitiation, or where the monomer (e.g.,acrylates, acrylic acid) is prone to polymerization. Those skilled inthe art are aware of the relative stability and readiness to polymerizeof the various monomers.

The stabilized monomer compositions of the present invention may alsocontain additional inhibitors, such as hydroquinone, the monomethylether of hydroquinone, (these often being required by monomerspecifications) or catechol, tert-butylated hydroquinones or catechols,other alkylated phenols, nitrosophenols and nitrosophenylhydroxylamines.

The stabilized compositions may also contain metal deactivators and UVabsorbers to improve light stability, stabilizers such as amines toretard acid-catalyzed degradation, thermal or photoinitiators, and/orother conventional additives.

When it is desired to subject the inhibited monomer to polymerization,the inhibitor can either be removed or overridden by sufficientpolymerization initiator. Removal can be accomplished by distillation,absorption or washing. The polymerization inhibiting action of theinstant compounds can be overridden by use of sufficient free radicalinitiator, actinic light (e.g., UV) irradiation, electron beam exposureor other polymerization initiating means.

The polymerization inhibitor is a heterocyclic moiety having a fivemember ring with nitrogen atoms in the first and third ring positions,and carbon atoms in the second, fourth and fifth positions.

The polymerization inhibitor has a structure as indicated by formula I:

wherein X is a substituent attached to the nitrogen atom in the firstring position and can be hydrogen (—H), hydroxyl (—OH), oxyl (—O•),nitro (—NO₂), or methyl (—CH₃).

R¹, R², R⁴ and R⁵ are the same or different and each is selected fromthe group consisting of hydrogen, an aliphatic moiety having from 1 toabout 20 carbon atoms, aryl, alkaryl or aralkyl having from 6 to about12 carbon atoms, alicyclic and heterocyclic, or wherein R¹ and R²together or R⁴ and R⁵ together form part of an alicyclic or heterocyclicmoiety having from about 4 to about 10 ring members.

R³ and optional group R⁶ (when present) are the same or different andeach is preferably selected from the group consisting of hydrogen and analiphatic moiety having from 1 to about 20 carbon atoms. Alternatively,R³ and optional group R⁶ together represent oxygen in the form of an oxo(═O) moiety. In yet another alternative, R³ and optional group R⁶ can bearyl, alkaryl or aralkyl having from 6 to about 12 carbon atoms,alicyclic or heterocyclic, or R³ and optional group R⁶ together can formpart of an alicyclic or heterocyclic moiety having from about 4 to about10 ring members.

The dotted lines each represent an optional supplemental bond, such thatwhere there is no optional supplemental bond within the ring (i.e., thenitrogen atom in the third ring position and the carbon atom in thefourth ring position are connected by a single bond) the R⁶ group ispresent as a ring substituent, z is 1 and Y is —H, —OH, or O•. Wherethere is an optional supplemental bond within the ring (i.e., thenitrogen atom in the third ring position and the carbon atom in thefourth ring position are connected by a double bond), there is no R⁶group present as a ring substituent, z is O or 1. That is, where z is 0the indicated nitrogen has no substituent attached to it. Where z is 1,Y is an oxygen atom (O) bonded to the ring nitrogen atom (N) as an oxide(N→O) moiety.

In one embodiment the polymerization inhibitor has a structure indicatedby formula II:

wherein X is selected from hydroxyl (—OH), hydrogen (—H), oxyl (—O•),nitro (—NO₂), and methyl (—CH₃).

The nitrogen atom in the third ring position is connected to the carbonatom in the fourth ring position by a double bond. Accordingly, thepresence of the oxide substituent (→O) attached to the second nitrogenatom in the third ring position is optional and there is no R⁶ group.

R¹, R², R³, R⁴ and R⁵ are as indicated above. Preferably R¹, R², R³, R⁴and R⁵ each selected from methyl, ethyl, propyl. or butyl groups, and Xis selected from hydroxyl or oxyl.

Exemplary compounds of formula II include (but are not limited to):2,2,4,5,5-pentamethyl-3-imidazoline;1-oxyl-2,2,4,5,5-pentamethyl-3-imidazoline-3-oxide;1-oxyl-4-ethyl-2,2,5,5-tetramethyl-3-imidazoline; 1-hydroxy-4-ethyl-2,2,5,5-tetramethyl-3-imidazoline;1-methyl-2,2,4,4-tetramethyl-3-imidazoline-3-oxide;1-hydroxy-2-(2,2,6,6-tetramethyl-piperidino-1-oxyl)-4,5,5-trimethyl-3-imidazoline;1-oxyl-2-cyclohexane-4-ethyl-5,5-dimethyl-3-imidazoline; and1-hydroxy-2,2,5,5-pentamethyl-3-imidazoline.

In another embodiment the polymerization inhibitor has a structure asindicated by formula Ill:

wherein R¹, R², R³, R⁶, R⁴, and R⁵ are as indicated above. X is asindicated above.

The nitrogen atom in the third ring position is connected to the carbonatom in the fourth ring position by a single bond. Accordingly, Y can behydrogen (—H), hydroxyl (—OH), or oxyl (—O•).

Preferably, R¹, R², R⁴ and R⁵ are each selected from the groupconsisting of methyl, ethyl, propyl, and butyl, and X is selected fromhydroxyl or oxyl. Optionally, R³ and R⁶ together form an oxo (═O) group.

Exemplary compounds of formula III include, (but are not limited to):1-oxyl-3-hydroxy-4-oxo-2,2,5,5-tetramethyl-3-imidazolidine, and1,3-dihydroxy-4-oxo-2,2,5,5-tetramethyl-3-imidazolidine.

In yet another feature of this invention the polymerization inhibitorcan include a blend made by mixing a first compound selected from thegroup consisting of 1-hydroxy-4-ethyl-2,2,5,5-tetramethyl-3-imidazoline,1-oxyl-2,2,4,5,5-pentamethyl-3-imidazoline-3-oxide, and1-hydroxy-2,2,4,5,5-pentamethyl-3-imidazoline, and a second compoundselected from the group consisting of1-oxyl-4-ethyl-2,2,5,5-tetramethyl-3-imidazoline and1-oxyl-2,2,4,5,5-pentamethyl-3-imidazoline.

Imidazolines and imidazolidines can be prepared in accordance with thefollowing outline of procedures:

In a first step a nitrosochloroalkane (Formula IV, below) can beprepared by reacting an alkene with sodium nitrite, hydrochloric acidand methanol.

The nitrosochloroalkane can then be reacted with hydroxylamine,hydrochloric acid and sodium acetate to produce a hydroxylamino oxime(Formula V, below).

The hydroxylamino oxime can then be reacted with a ketone to produce amixture of an hydroxyl and oxyl imidazoline oxide (Formulas IIa and IIe,below), which can then be oxidized by manganese dioxide (MnO₂) toproduce oxyl imidazoline oxide (Formula IIb, below), which can bereduced by hydroxylamine to form pure hydroxylimidazoline.

Alternatively, the hydroxyl imidazoline oxide can be reacted with sodiumborohydride to produce a dihydroxyl imidazolidine (Formula IIIa, below).The oxyl imidazoline oxide can be reacted with sodium borohydride toproduce an oxyl hydroxyimidazolidine (Formula IIIb).

Alternatively, the hydroxylamino oxime can be reacted with concentratedhydrochloric acid and water to produce hydroxylamino ketone. Thehydroxylamino ketone can then be reacted with a ketone and ammoniumhydroxide to produce a mixture compounds of formulas IIc, IId and IIe,below, which can then be oxidized with MnO₂ to produce oxyl imidazoline(Formula IId, below).

The following examples are presented for the purpose of illustrationonly and are not to be construed as limiting the present invention.

EXAMPLE 1

Preparation of a nitrosochloroalkane from an alkene was accomplished bycharging 72.3 g sodium nitrite and 360 ml. methanol to a flask andcooling the mixture to −15.3° C. Then 41.9 g of trimethylethylene(2-methyl-2-butene) was added and the mixture was cooled to −19.8° C.244.7 ml hydrochloric acid (36% concentration HCl) was added over aperiod of 2 hrs. after which the mixture was allowed to react for 4 hrsat a temperature between −15.2° C. and −19.5° C. Afterwards the mixturewas poured into iced water, washed and filtered. The product was 81.3 gof 2-chloro-2-methyl-3-nitrosobutane.

EXAMPLE 2

Preparation of an hydroxylamino oxime from a nitrosochloroalkane wasaccomplished by preparing an aqueous first solution (0.504 g/ml) ofhydroxylamine hydrochloride (NH₂OH.HCl/H₂O), mixing 112 ml isopropanolin water to achieve a 0.8025 g/ml solution which was then used todissolve 60.5 g sodium acetate to achieve a 0. 1025 g/ml second solutionof CH₃COONa/CH₃CHOHCH₃—H₂O. The first and second solutions were thencombined in a flask at ambient temperature and 50 g of2-chloro-2-methyl-3-nitrosobutane were added to flask. The contents ofthe flask were reacted at 67.1 ° C. for 2.5 hrs. The mixture was allowedto remain in the flask overnight. The isopropanol was then removed undervacuum and heat. The resulting filtered and washed product was 53.5 g2-hydroxylamino-2-methyl-3-oximebutane acetate.

EXAMPLE 3

Preparation of a mixture of an oxylimidazoline oxide andhydroxyimidazoline oxide from a hydroxylamino oxime was accomplished bymixing 50.07 g 2-hydroxylamino-2-methyl-3-oximepentane acetate, 500 mlacetone, and 10 ml hydrochloric acid (5% concentration) in a flask,refluxing for 24 hrs. 25 min. at 58° C., evaporating the solvent, thenrefrigerating the flask adding an equal volume of ether, filtering,rinsing with ether and drying. The product was 8.5 g of a mixturecontaining 52.4% of1-hydroxy-4-ethyl-2,2,5,5-tetramethyl-3-imidazoline-3-oxide and 43.2% of1-oxyl-4-ethyl-2,2,5,5-tetramethyl-3-imidazoline-3-oxide.

EXAMPLE 4

Preparation of an oxyl imidazoline oxide from a hydroxyl imidazolineoxide was achieved by combining 50.0 g of the product mixture producedin accordance with Example 3, 20 g MnO₂ and 500 ml ethyl acetate in aflask at room temperature, stirring for 1 hr 15 min., filtering twice,evaporating the ethyl acetate, drying and recrystallizing with ethylacetate. The product was 54.51 g of1-oxyl-2,2,4,5,5-pentamethyl-3-imidazoline-3-oxide.

EXAMPLE 5

Preparation of a hydroxylamino ketone from an hydroxylamino oxime wasachieved by mixing 50 g of 2-hydroxylamino-2-methyl-3-oximebutaneacetate and 100 ml of hydrochloric acid (36% concentration) in a flask,allowing the mixture to react for 20-22 hrs at −5° C. The product wasthen filtered, rinsed with distilled water, dried by evaporation thenrecrystallized from an acrylonitrile solvent. A product of 35 g of2-hydroxylamino-2-methyl-3-butanone was obtained.

EXAMPLE 6

Preparation of a mixture of an oxylimidazoline and hydroxylimidazolinefrom an hydroxylamino ketone was achieved by mixing 10.0 g of2-hydroxylamino-2-methyl-3-pentanone hydrochloride and 50 ml acetone ina flask, adding 20 ml ammonium hydroxide (30% concentration), stirringat room temperature for 1 hr, then evaporating the acetone. The flaskwas then refrigerated overnight and the crystals of product werefiltered and dried. The product was 1.3 g of a mixture containing 55.1 %of 1-hydroxy-4-ethyl-2,2,5,5-tetramethyl-3-imidazoline and 42.1 % of1-oxyl-4-ethyl-2,2,5,5-tetramethyl-3-imidazoline.

EXAMPLE 7

Preparation of an oxyl imidazoline from an hydroxylamino ketone wasachieved by mixing 16.5 g of 2-hydroxylamino-2-methyl-3-pentanonehydrochloride, 19.6 g of cyclohexanone, and 29 ml of ammonium hydroxide(30% concentration) in a flask while maintaining the flask at roomtemperature for 1 hr. The contents of the flask were then extracted withether. The ether layer was separated and MgSO₄ was added to the ether asa drying agent. The MgSO₄ was then filtered out. Then, the ethersolution was oxidized by 2.1 g MnO₂ for 1 hr., filtered, then dried byevaporation to remove ether and water. Additional ether and 8 mldeionized water were added and the layers of liquid were separated.MgSO₄ was added to the organic layer, which was then stirred for 1 hr.and filtered out. The ether was removed by evaporation from the liquid,which was then refrigerated at −7° C. to crystallize. A product of 9.25g of 2-cyclohexanone-4-ethyl-5,5-dimethyl-3-imidazoline-1-oxyl wasobtained.

EXAMPLE 8

2 g of the amide of1-oxyl-2,2,5,5-tetramethyl-3-oxide-3-imidazoline-4-carbonic acid(Formula VIa, below) was dissolved in 25 ml of 10% KOH, then 1.2 g NaBrOwas added and the mixture was stirred for 4 hrs. The resulting compoundwas 1-oxyl-3-hydroxy-4-oxo-2,2,5,5-tetramethyl-3-imidazolidine (FormulaVIb), which was then extracted with ethyl acetate. The solution wasdried with MgSO₄ and evaporated. 1 g of compound Vb was then furtherreduced by 0.5 g hydroxylamine in 25 ml ether to form 0.7 g of1,3-dihydroxy-4-oxo-2,2,5,5-tetramethyl-3-imidazolidine having FormulaVIc, below.

EXAMPLE 9

10 g of 1-oxyl-2,2,4,5,5-pentamethyl-3-imidazoline was dissolved in 100ml of dried ether and 4 g of hydroxylamine were added. The mixture wasstirred for 5 hrs, dried with MgSO₄ and the ether was then evaporated.The product 8.2 g of 1-hydroxy-2,2,4,5,5-pentamethyl-3-imidazoline wasrecrystallized from ethylacetate.

EXAMPLES 10-19

In these examples the effectiveness of the polymerization inhibitors ofthe present invention in preventing polymerization of styrene wasmeasured. The styrene was purified to remove all traces of tert-butylcatechol (TBC). All of the samples were tested in accordance with thefollowing procedure:

A 40 g test quantity of TBC-free styrene containing 100 ppm of inhibitorwas charged to a three neck 50ml round bottom flask fitted with athermometer and a reflux condenser whose top opening was fitted with aseptum through which an 18 gauge syringe needle was inserted. The flaskwas also fitted with a gas inlet tube and a magnetic stirrer. A constanttemperature silicone oil bath was used to control the temperature. Thestyrene was prepurged with nitrogen to remove dissolved oxygen prior tobeing heated in the oil bath.

When the styrene reached the desired temperature of 116° C. air wassparged into the flask at 5 cc/min. Samples of the test styrene wereremoved at regular intervals of time and the refractive index of thestyrene was measured to determine the polymer content. The relativeeffectiveness of inhibition of the various polymerization inhibitorstested is reported in terms of an induction period, which is the lengthof time elapsed before the level of polymer in the styrene sample hasreached 1% or higher. Thus, the longer the induction period the moreeffective was the polymerization inhibitor.

The results are set forth below in Table 1. Multiple sampling resultsare shown for some examples.

TABLE 1 Induc- tion % Time Poly- Exmpl. Inhibitor (min) mer 101-oxyl-2,2,4,5,5-pentamethyl-3-imidazoline 81 1.5 111-oxyl-2,2,4,5,5-pentamethyl-3-imidazoline-3- 71 1.33 oxide 121-oxyl-4-ethyl-2,2,5,5-tetramethyl-3- 61 1.5 imidazoline 65 2.49 13mixture of 1-hydroxy-4-ethyl-2,2,5,5- 73 1.0 tetramethyl-3-imidazoline(40-45%) and 1- 78 1.0 oxyl-4-ethyl-2,2,5,5-tetramethyl-3-imidazoline 751.33 (40-45%) 14 1,2,2,5,5-pentamethyl-3-imidazoline-3-oxide 20 2.66 151-nitro-2,2,5,5-tetramethyl-3-imidazoline-3- 18 1.99 oxide 161-hydroxy-2-(2,2,6,6-tetramethyl-piperidino-1- 88 1.33oxyl)-4,5,5-trimethyl-3-imidazoline 171-oxyl-2-cyclohexane-4-ethyl-5,5-dimethyl-3- 58 1.83 imidazoline 18mixture of 1-hydroxy-2,2,4,5,5-pentamethyl-3- 62 1.83 imidazoline(51.9-55.1%) and 1-oxyl- 96 1.99 2,2,4,5,5-pentamethyl-3-imidazoline 991.83 (31.2%-34.2%) 19 1,3-dihydroxy-2,2,4,5,5-pentamethyl-3- 58 4.82imidazolidine

EXAMPLE 20

A first blend was made by premixing 1 part1-hydroxy-2,2,4,5,5-pentamethyl-3-imidazoline and 1 part1-oxyl-2,2,4,5,5-pentamethyl-3-imidazoline with heating to a temperatureof 50° C. This blend was then tested for polymerization inhibition ofstyrene in accordance with the method of Examples 10-19. The blendexhibited an induction time of 97 minutes with a corresponding polymerlevel of 1.33%.

A second blend of the same composition percentages as the first blendand made in the same manner exhibited an induction time of 95 minuteswith a corresponding polymer level of 1.66%.

A third blend of the same composition percentages as the first blend andmade in the same manner exhibited an induction time of 76 minutes and acorresponding polymer level of 1.66%.

EXAMPLE 21

1 part 1-hydroxy-2,2,4,5,5-pentamethyl-3-imidazoline and 1 part1-oxyl-2,2,4,5,5-pentamethyl-3-imidazoline were mixed in situ in a testsample of styrene to a concentration of 100 ppm of blended inhibitor,which was then tested for polymerization inhibition in accordance withthe method of Examples 10-19. The blend exhibited an induction time of81 minutes with a corresponding polymer level of 1.66%.

EXAMPLE 22

1 part 1-hydroxy-2,2,4,5,5-pentamethyl-3-imidazoline and 2 parts1-oxyl-2,2,4,5,5-pentamethyl-3-imidazoline were mixed in situ in a testsample of styrene to a concentration of 100 ppm of blended inhibitor,which was then tested for polymerization inhibition in accordance withthe method of Examples 10-19. The blend exhibited an induction time of82 minutes with a corresponding polymer level of 1.66%.

EXAMPLE 23

A blend was made by premixing 1 part1-hydroxy-2,2,4,5,5-pentamethyl-3-imidazoline and 2 parts1-oxyl-2,2,4,5,5-pentamethyl-3-imidazoline with heating at a temperatureof 50° C. This blend was then tested for polymerization inhibition ofstyrene in accordance with the method of Examples 10-19. The blendexhibited an induction time of 78 minutes with a corresponding polymerlevel of 1.00%.

EXAMPLE 24

2 parts 1-hydroxy-2,2,4,5,5-pentamethyl-3-imidazoline and 1 part1-oxyl-2,2,4,5,5-pentamethyl-3-imidazoline were mixed in situ in a testsample of styrene to a concentration of 100 ppm of blended inhibitor,which was then tested for polymerization inhibition in accordance withthe method of Examples 10-19. The blend exhibited an induction time of87 minutes with a corresponding polymer level of 1.50%.

EXAMPLE 25

3 parts 1-hydroxy-2,2,4,5,5-pentamethyl-3-imidazoline and 1 part1-oxyl-2,2,4,5,5-pentamethyl-3-imidazoline were mixed in situ in a testsample of styrene to a concentration of 100 ppm of blended inhibitor,which was then tested for polymerization inhibition in accordance withthe method of Examples 10-19. The blend exhibited an induction time of78 minutes with a corresponding polymer level of 1.83%.

EXAMPLE 26

A blend was made by premixing 1 part1-oxyl-2,2,4,5,5-pentamethyl-3-imidazoline and 1 part1-oxyl-2,2,4,5,5-pentamethyl-3-imidazoline-3-oxide with heating at atemperature of 50° C. This blend was then tested for polymerizationinhibition of styrene in accordance with the method of Examples 10-19.The blend exhibited an induction time of 69 minutes with a correspondingpolymer level of 1.50%.

EXAMPLE 27

A first blend was made by premixing 1 part1-hydroxy-4-ethyl-2,2,5,5-tetramethyl-3-imidazoline and 1 part1-oxyl-4-ethyl-2,2,5,5-tetramethyl-3-imidazoline. This blend was thentested for polymerization inhibition of styrene in accordance with themethod of Examples 10-19. The blend exhibited an induction time of 60minutes with a corresponding polymer level of 1.00%.

A second blend of the same composition percentages as the first blendand made in the same manner exhibited an induction time of 71 minuteswith a corresponding polymer level of 1.00%.

COMPARATIVE EXAMPLE

For purposes of comparison the effectiveness of 2,6-dinitro-p-cresol(DNPC), a known polymerization inhibitor, was tested for polymerizationinhibition of styrene in accordance with the method of Examples 10-19described above. The DNPC exhibited an induction time of 60 minutes fora corresponding polymerization level of 1.00 %.

While the above description contains many specifics, these specificsshould not be construed as limitations on the scope of the invention,but merely as exemplifications of preferred embodiments thereof. Thoseskilled in the art will envision many other possible variations withinthe scope and spirit of the claims appended hereto.

What is claimed is:
 1. A method for stabilizing a polymerizableethylenically unsaturated organic compound from prematurepolymerization, comprising: adding to the unsaturated organic compoundan effective amount for premature polymerization inhibition, of apolymerization inhibitor including at least one compound having theformula:

 wherein X is —H, —OH, —O•, —NO₂, or —CH₃, R¹, R², R⁴ and R⁵ are thesame or different and each is selected from the group consisting ofhydrogen, an aliphatic moiety having from 1 to about 20 carbon atoms,aryl, alkaryl or aralkyl having from 6 to about 12 carbon atoms,alicyclic and heterocyclic, or R¹ and R² together or R4 and R⁵ togetherform part of an alicyclic or heterocyclic moiety having from about 4 toabout 10 ring members, R³ is hydrogen or an aliphatic moiety having from1 to about 20 carbon atoms, and z is 0 or 1 and where z is 1, Y is Obonded to N in the form of an N→O moiety, wherein the unsaturatedorganic compound is selected from the group consisting of styrene,methylstyrene, divinylbenzene, butadiene, isoprene, vinyl chloride,chloroprene, vinylidene chloride, vinylidene fluoride, vinyl fluoride,acrylic acid, methacrylic acid, crotonic acid, vinyl acetate, methylmethacrylate, ethyl acrylate, methyl acrylate, 2-hydroxyethyl acrylate,2-hydroxyethyl methacrylate, ethylene bismethacrylate,trimethylolpropane triacrylate, acrylated epoxy resin, polyethyleneglycol diacrylate, acrylamide, N,N-dimethylacrylamide,methylene-bisacrylamide, N-vinylpyrrolidone, acrylonitrile, methyl vinylether, vinyl pyridine, diethyl vinylphosphonate and sodiumstyrenesulfonate.
 2. The method of claim 1 wherein the polymerizationinhibitor includes a compound selected from the group consisting of1-oxyl-2,2,4,5,5-pentamethyl-3-imidazoline,1-hydroxy-2,2,4,5,5-pentamethyl-3-imidazoline,1-oxyl-4-ethyl-2,2,5,5-tetramethyl-3-imidazoline,1-hydroxy-4-ethyl-2,2,5,5-tetramethyl-3-imidazoline,1-oxyl-2,2,4,5,5-pentamethyl-3-imidazoline-3-oxide,1,2,2,5,5-pentamethyl-3-imidazoline-3-oxide,1-nitro-2,2,5,5-tetramethyl-3-imidazoline-3-oxide,1-hydroxy-2-(2,2,6,6-tetramethyl-piperidino-1-oxyl)-4,5,5-trimethyl-3-imidazoline,1-oxyl-2-cyclohexane-4-ethyl-5,5-dimethyl-3-imidazoline, and mixturesthereof.
 3. The method of claim 1 wherein the unsaturated organiccompound is styrene.
 4. The method of claim 1 wherein unsaturatedorganic compound is neat.
 5. The method of claim 1 wherein theunsaturated organic compound is mixed with a solvent.
 6. The method ofclaim 5 wherein the solvent is selected from the group consisting oftoluene, benzene, ethylbenzene, styrene and water.
 7. The method ofclaim 1 wherein the effective amount of the polymerization inhibitorcompound having formula (I) ranges from a concentration of about 1 ppmto 10,000 ppm by weight.
 8. The method of claim 1 wherein R¹, R², R³,R⁴, and R⁵, are each a moiety selected from the group consisting ofmethyl, ethyl, propyl and butyl, and X is —OH or —O•.
 9. The method ofclaim 8 wherein the polymerization inhibitor includes a mixture of atleast first and second compounds having formula (I) wherein in saidfirst compound X is —OH, and z is 0, and in said second compound X is—O• and z is
 0. 10. The method of claim 9 wherein said first compound isselected from the group consisting of1-hydroxy-4-ethyl-2,2,5,5-tetramethyl-3-imidazoline and1-hydroxy-2,2,4,5,5-pentamethyl-3-imidazoline, and the second compoundis selected from the group consisting of1-oxyl-4-ethyl-2,2,5,5-tetramethyl-3-imidazoline and1-oxyl-2,2,4,5,5-pentamethyl-3-imidazoline.
 11. The method of claim 8further including the step of mixing a first compound selected from thegroup consisting of 1-hydroxy-2,2,4,5,5-pentamethyl-3-imidazoline,1-hydroxy-4-ethyl-2,2,5,5-tetramethyl-3-imidazoline and1-oxyl-2,2,4,5,5-pentamethyl-3-imidazoline-3-oxide, with a secondcompound selected from the group consisting of1-oxyl-2,2,4,5,5-pentamethyl-3-imidazoline and1-oxyl-4-ethyl-2,2,5,5-tetramethyl-3-imidazoline, to produce thepolymerization inhibitor.
 12. The method of claim 11 wherein the step ofmixing the first compound with the second compound is performed prior toadding the polymerization inhibitor to the unsaturated organic compound.13. The method of claim 12 wherein the step of mixing the first compoundwith the second compound is performed while heating the mixture.
 14. Amonomer composition stabilized against premature polymerization whichincludes: a) an ethylenically unsaturated organic monomer; and b) aneffective amount for premature polymerization inhibition of component(a), of a polymerization inhibitor including at least one compoundhaving the formula:

 wherein X is —H, —OH, —O•, —NO₂, or —CH₃, R¹, R², R⁴ and R⁵ are thesame or different and each is selected from the group consisting ofhydrogen, an aliphatic moiety having from 1 to about 20 carbon atoms,aryl, alkaryl or aralkyl having from 6 to about 12 carbon atoms,alicyclic and heterocyclic, or wherein R¹ and R² together form part ofan alicyclic or heterocyclic moiety having from about 4 to about 10 ringmembers, R³ is hydrogen or an aliphatic moiety having from 1 to about 20carbon atoms, and z is 0 or 1 and where z is 1, Y is O bonded to N inthe form of an N→O moiety, wherein the unsaturated organic monomer is acompound selected from the group consisting of styrene, methylstyrene,divinylbenzene, butadiene, isoprene, vinyl chloride, chloroprene,vinylidene chloride, vinylidene fluoride, vinyl fluoride, acrylic acid,methacrylic acid, crotonic acid, vinyl acetate, methyl methacrylate,ethyl acrylate, methyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxyethylmethacrylate, ethylene bismethacrylate, trimethylolpropane triacrylate,acrylated epoxy resin, polyethylene glycol diacrylate, acrylamide,N,N-dimethylacrylamide, methylene-bisacrylamide, N-vinylpyrrolidone,acrylonitrile, methyl vinyl ether, vinyl pyridine, diethylvinylphosphonate and sodium styrenesulfonate.
 15. The method of claim 13wherein the mixture is heated to 50° C.
 16. The composition of claim 14wherein the unsaturated organic monomer is styrene.
 17. The compositionof claim 14 wherein the effective amount of the polymerization inhibitorcompound having formula (I) ranges from a concentration of about 1 ppmto 10,000 ppm by weight.
 18. The method of claim 16 wherein the firstcompound and second compound are mixed in situ in the unsaturatedorganic compound.
 19. The composition of claim 18 wherein R¹, R², R³,R⁴, and R⁵, are each a moiety selected from the group consisting ofmethyl, ethyl, propyl and butyl groups, and X is —OH or —O•.
 20. Themethod of claim 19 wherein the polymerization inhibitor includes amixture of at least first and second compounds having formula (I)wherein in said first compound X is —OH, and z is 0, and in said secondcompound X is —O• and z is
 0. 21. The method of claim 20 wherein saidfirst compound is selected from the group consisting of1-hydroxy-4-ethyl-2,2,5,5-tetramethyl-3-imidazoline and1-hydroxy-2,2,4,5,5-pentamethyl-3-imidazoline, and the second compoundis selected from the group consisting of1-oxyl-4-ethyl-2,2,5,5-tetramethyl-3-imidazoline and1-oxyl-2,2,4,5,5-pentamethyl-3-imidazoline.
 22. The method of claim 11wherein from 1 to 3 parts of the first compound are mixed with from 1 to2 parts of the second compound.
 23. The composition of claim 14 whereinthe polymerization inhibitor includes a compound selected from the groupconsisting of 1-oxyl-2,2,4,5,5-pentamethyl-3-imidazoline,1-hydroxy-2,2,4,5,5-pentamethyl-3-imidazoline,1-oxyl-4-ethyl-2,2,5,5-tetramethyl-3-imidazoline,1-hydroxy-4-ethyl-2,2,5,5-tetramethyl-3-imidazoline,1-oxyl-2,2,4,5,5-pentamethyl-3-imidazoline-3-oxide,1,2,2,5,5-pentamethyl-3-imidazoline-3-oxide,1-nitro-2,2,5,5-tetramethyl-3-imidazoline-3-oxide,1-hydroxy-2-(2,2,6,6-tetramethyl-piperidino-1-oxyl)-4,5,5-trimethyl-3-imidazoline,1-oxyl-2-cyclohexane-4-ethyl-5,5-dimethyl-3-imidazoline, and blendsthereof.
 24. The composition of claim 14 further including one or moreadditives selected from the group consisting of metal deactivators, UVabsorbers, stabilizers to retard acid-catalyzed degradation, thermalinitiators and photoinitiators.